The HIV-1 Rev-RRE is well known but not completely understood. It is known that genes encoding HIV structural proteins, i.e. HIV genes gag, pol and env each contain an RRE which is recognized by HIV protein Rev. These sequences are known to interact with the HIV protein Rev. Nucleic acid molecules in cells that contain the RRE bind to Rev that is present in the cell and are transported to the cytoplasm. This transport results in a higher level of gene expression relative to that observed in the absence of the RRE or Rev in similar constructs. U.S. Pat. Nos. 5,554,528 and 5,604,114, which are incorporated herein by reference, disclose HIV RRE sequences. U.S. Pat. Nos. 5,650,309 and 5,665,577, which are incorporated herein by reference, disclose vectors that comprise HIV RRE sequences.
The CTE system is well known and described in, inter alia, U.S. Pat. Nos. 5,585,263 and 5,880,276, which are each incorporated herein by reference. According to this system, host proteins recognize the CTE sequence on the mRNA and transport it from the nucleus to the cytoplasm. This transport results in a higher level of gene expression relative to that observed in the absence of the RRE or Rev in similar constructs. CTE systems are also described in Bray, M., S. Prasad, J. W. Dubay, E. Hunter, K.-T. Jeang, D. Rekosh, and M.-L. Hammarskjold (1994). A small element from the Mason-Pfizer monkey virus genome makes human immunodeficiency virus type 1 expression and replication Rev-independent. Proc. Natl. Acad. Sci. USA 91:1256-1260; Saavedra, C., B. Felber, and E. Izaurralde. 1997. The simian retrovirus-1 constitutive transport element, unlike the HIV-1 RRE, utilises factors required for the export of cellular mRNAs. Curr. Biol. 619-628, Ernst R K, Bray M, Rekosh D, Hammarskgold M L. (1997) Secondary structure and mutational analysis of the Mason-Pfizer monkey virus RNA constitutive transport element. RNA. 3(2):210-22; and Kang Y, Bogerd H P, Cullen B R. (2000). Analysis of cellular factors that mediate nuclear export of RNAs bearing the Mason-Pfizer monkey virus constitutive transport element. J Virol. 74(13):5863-71, which are each incorporated herein by reference.
There is a need to provide improved systems for enhancing expression of coding sequences in nucleic acid molecules. There is a need to provide improved vaccines, immunization methods, and gene therapy methods and compositions that exhibit high levels of expression of coding sequences in nucleic acid molecules.